SATELLITE TV Ku-BAND FREQUENTLY ASKED QUESTIONS
Robert Smathers (roberts@nmia.com), author
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UPDATED 10/04/2002
WHAT IS ON Ku-BAND?
There are various types of services on Ku-band. Some of the services
include NBC, news feeds, Satellite News Gathering mobile truck uplinks,
educational networks, teleconferences, sports backhauls, various other
backhauls, international programming, business networks, Single Channel
Per Carrier analog audio transmissions and FM Squared audio services.
WHAT IS INVOLVED IN A Ku-BAND UPGRADE?
If you have an existing C-band system, you will need to check the mesh on
your dish if you have a mesh dish. You will also need to purchase a
Ku-band LNB and a C/Ku-band feedhorn, and have some coax for the Ku-band
LNB.
WHAT DISH TYPE IS BEST?
A dish that is a one piece or very few pieces. It is better to have a 4
section dish than it is an 8 section or more. The smaller the number of
sections, the better parabola shape you have and also the harder it would
be to warp the dish (because of the smaller number of seams
where the sections come together).
With the new generation of powerful Ku-band satellites, one can also
get away with a smaller dish, such as a 3 foot, single piece, offset-fed
dish. That dish works great for the international services on Telstar 5
Ku-band, Galaxy 10R Ku-band, and for sports backhauls on various Ku-band
satellites throughout the arc.
WHAT DISH MOUNT TYPE IS BEST?
The Horizon-to-Horizon dish mount is the better than a polar mount
for Ku-band. Ku-band requires the system to be well aimed and to follow
the arc, and the horizon-to-horizon mount follows the whole arc much better
than a polar mount.
For the 3 foot, one piece dishes, the mount is typically a ring or
patio mount, so the user has to adjust both elevation and azimuth
to move from satellite to satellite and aiming can become a little
tricky at times.
WHAT SUPPORT IS BEST?
The tri or quad supports are best -- they'll keep the Ku-band feedhorn
really stable so winds don't affect critical Ku-band reception. A
buttonhook feed can move in the wind and you can easily lose Ku-band
reception. It is best to put guy-wires on the buttonhook feed for support
if you can't get a tri or quad support.
WILL MY SATELLITE DISH WORK FOR Ku-BAND?
If you have a solid dish, you should be fine as far as compatibility.
If you have a mesh dish, you will have to run a test to see if Ku-band
could be done. The test is very simple. You need to measure the "holes"
in the mesh. If they are 1/4" or larger, chances are your dish won't
reflect Ku-band signals too well and you might want to consider getting a
new mesh dish where the hole size is smaller.
WHAT KIND OF SATELLITE RECEIVER WILL WORK?
For analog reception:
You will need a receiver whose IF Block input frequency will match that of
a Ku-band LNB. Once you have that matched, you will also need to have the
ability to invert the picture polarity as well as tune the Ku-band LNB
signal. There is no standard layout for the Ku-band satellites. One type
of satellite will usually have a different uplink/downlink frequency format
than another type (GSTAR vs. Telstar 400 series, for example).
For digital reception:
By far the most common digital format used on the Ku-band is DVB using
the main profile video format. Some transmissions use the studio profile
video format (please consult the FAQ in the "Other Info-files" section
for more information about main profile vs. studio profile DVB video.
Consumer receivers for DVB can be had for as little as around $200 new.
One can even find some receivers in the secondary market for less than
that.
Several public television stations are fed on Ku-band in Digicipher II
format. One can use a commercial Digicipher II receiver, a 4DTV full-
blown receiver, or even the 4DTV sidecar receiver to receive some PBS
stations.
WILL A WARPED DISH WORK?
No. You need to have a very parabolic dish. Warpage will cause
signal mis-reflection and you won't be getting the best performance
out of your system. To check your dish for warpage, you will need to get
some string and some tape. Take one string and stretch it as tight as you
can and anchor it to the dish edges with the tape. Make this string go
"north" and "south" across the face of your dish. Do the same thing with
the other string, yet go "east" and "west" across the face of the dish.
Make sure both strings are tight. If the strings do not come together in
the center, then your dish is warped and you will need to find some way to
take the warp out for maximum performance. If the strings touch in the
center, your dish looks very good as far as not being warped.
WHAT TO DO IF I DON'T HAVE A Ku-BAND CABLE?
For any upgrade to Ku-band, you will need another length of coax cable to
go from your Ku-band LNB to your satellite receiver.
WHAT TYPE OF CABLE SHOULD I USE?
I prefer to use RG-6 since it has pretty good low loss figures at the
950-1450 frequencies that your Ku-band LNB will be sending to your
receiver. RG-59 works okay if you cannot easily find RG-6 or if you
don't want to spend a few more cents a foot on the RG-6 coax.
WHAT ABOUT INSTALLATION? (F/D ADJUSTMENT)
The best advice is to follow the instructions that come with the dual-band
feedhorn. From the instructions I've seen (for a Chaparral and an ADL
feedhorn), you want to first measure your dish's F/D (focal length over
diameter) and slide the throat of the feedhorn through the scaler ring and
tighten it down where the F/D ratio marked on the throat matches up with
the marking on the scaler ring that it has to.
WHAT ABOUT INSTALLATION? (FOCAL LENGTH ADJUSTMENT)
Once you have set the throat/scaler ring assembly to the right F/D ratio,
you want to attach the feedhorn to the support (quad, tri, or buttonhook)
and, without disturbing the F/D setting you did in step 4a above, move
the feedhorn in and out until the focal length is set. You want the focal
length to equal the length from the center of the dish to about 1/8" inside
the throat of the feedhorn. Tighten down the feedhorn to the support once
you have set the focal length.
WHAT ABOUT INSTALLATION? (CENTERING)
The final step in the process is to make sure you feedhorn is centered in
aiming into the dish. There are various gadgets to do this (one being a
laser pointer to tell you where the feedhorn is pointed to), but I have had
great luck doing the F/D ratio and the focal adjustment correctly and then
"eyeball"ing the centering part to make sure it looks like it is properly
centered.
WHAT ABOUT INSTALLATION? (RE-TRACKING THE ARC)
In many cases, you will have to retrack the dish. Ku-band has a smaller
wavelength signal, and therefore it is not as forgiving for reception as a
C-band signal is.
That provides a benefit. It is best to use the Ku-band when tracking a
dish because of its unforgiveness. Once you track up a dish perfectly on
Ku-band, you will also have very good tracking on C-band as well.
I prefer the three satellite method of tracking due to its simplicity.
What you first do is peak your dish on the satellite due south of you.
After that is done, you move you dish to a satellite that is as far east as
you can see and peak up on that. Make a mark on the elevation adjustment
screw. Move your dish back to the center satellite and peak up on it
again. Next, move your dish to the extreme western Ku-band satellite you
can get and peak on it. Make another mark. The final step involves you
finding the center of the two marks and setting your elevation adjustment.
That is a very good, easy-to-do method of tracking for do-it-yourselfers.
WHAT ABOUT Ku-BAND FREQUENCIES/FORMATS?
There are many various formats for the Ku-band satellites. Any good
reference book or satellite channel chart will have a list of these
satellite formats and the downlink frequencies.
TROUBLE-SHOOTING: WHAT IF I DON'T GET A SIGNAL?
No signal could mean (and the suggested solution):
1) You are not tracking the arc -- check the tracking of your dish
2) You are not on a Ku-band satellite -- move your dish east and west
in search of a Ku-band satellite
3) Water in your feedhorn -- make sure there is no water in the
feedhorn throat or waveguides -- water is a good signal blocker
4) Coax cable bad -- make sure the cable is continuous and not
chopped or have rusted wires. Check and make sure the connectors
are still on properly and are not rusted, loose, etc.
5) Improper focal length -- check your focal length
6) Your Ku-band LNB is bad. Borrow a friend's LNB or have someone
hook up your LNB to see if it works on their system.
TROUBLE-SHOOTING: WHAT IF I GET A C-BAND SIGNAL?
You have the wrong coax connected to your Ku-band input. With
your C-band LNB connected to the Ku-band input, you'll get
inverse video C-band signals that will show up on channels they are not
supposed to be on. A switch of the C and Ku-band cables should get
the cable to the right input and correct that problem.
TROUBLE SHOOTING: WHAT ABOUT A WEAK SIGNAL?
A weak signal could result from the feedhorn not centered, the focal length
wrong, you not being right on the arc, you not being right on a Ku-band
satellite, a cable that is slowly going bad, water in the feedhorn, nests
in the feedhorn among other factors.
WHAT PROBLEMS OCCUR IN Ku-BAND RECEPTION WITH A PERFECT ALIGNED SYSTEM?
The major problem with Ku-band reception with a perfect aligned system is
rain fade and what I call "snow fade". "Snow fade" is what I call the
situation when snow accumulates on a dish and changes the focal point of
the dish. The focal point affects Ku-band much more than C-band (since you
have some tolerance in reception of C-band signals). Another problem is
the wind -- you can be right on a Ku-band satellite and a gust of wind can
come and move your dish off of the satellite. Horizon-to-horizon mounts
are better fighters of wind gusts than polar mount systems are.
WHAT IF I HAVE ANY MORE QUESTIONS?
You can write me at roberts@nmia.com.